Pumps for pumping molten metal are used in furnaces in the production of metal articles. Common functions of pumps are circulation of molten metal in the furnace or transfer of molten metal to remote locations along transfer conduits or risers that extend from a base of the pump to the remote location.
Currently, many metal die casting facilities employ a main hearth containing the majority of the molten metal. Solid bars of metal may be periodically melted in the main hearth. A transfer pump is located in a separate well adjacent the main hearth. The transfer pump draws molten metal from the well in which it resides and transfers it into a ladle or conduit and from there to die casters that form the metal articles. The present invention relates to pumps used to transfer molten metal from a furnace to a die casting machine, ingot mould, DC caster or the like.
A traditional molten metal transfer pump is described in U.S. Pat. No. 6,286,163, the disclosure of which is herein incorporated by reference. Referring to FIG. 1, the molten metal pump is indicated generally by the reference numeral 10. The pump 10 is adapted to be immersed in molten metal contained within a vessel 12. The vessel 12 can be any container containing molten metal, although the vessel 12 as illustrated is an external well of a reverberatory furnace 13. The pump 10 has a base member 14 within which an impeller (not shown) is disposed. The impeller includes an opening along its bottom or top surface that defines a fluid inlet for the pump 10. The impeller is supported for rotation within the base member 14 by means of an elongate, rotatable shaft 18. The upper end of the shaft 18 is connected to a motor 20. The base member 14 includes an outlet passageway connected to a riser 24. A flanged pipe 26 is connected to the upper end of the riser 24 for discharging molten metal into a spout or other conduit (not shown). The pump 10 thus described is so-called transfer pump, that is, it transfers molten metal from the vessel 12 to a location outside of the vessel 12.
Another exemplary transfer pump is described in CA 2284985. The pump consists of two main parts, an upper tube portion which is suspended above the molten magnesium bath during operation and lower tube portion which is immersed in the bath. A motor is positioned at the top of the upper portion. A coupling attaches an auger shaft to the motor. The coupling holds the weight of the auger shaft and positions it in place inside the tube. The auger shaft is centered within the internal diameter of the two portions, running the length of both, and is held in position by a set of guide bearings. The lower portion is comprised of a cylindrical casing in which the auger is located and aligned. Several inlet holes are located in the walls of the cylindrical casing. A second set of inlet holes in the cylindrical casing are located near the base of the pump. These inlet holes permit the surrounding molten metal to enter the pump.
The auger comprises a shaft, upon which are welded flutes. The pitch of the flutes preferably varies between 2 to 4 inches. The auger acts like a positive displacement pump. The rotation of the auger shaft by the motor supplies a steady force to the molten magnesium, forcing the molten liquid to the bottom of the pump and out of an elbow shaped connector located at the outlet end of the cylindrical casing at the base of the pump. The molten magnesium displaced to the bottom of the pump is downwardly forced out through the connector by means of the rotation of the auger. The connector is attached to a heated transfer tube which will convey the molten magnesium from the holding furnace to the die of a casting machine.
A further alternative transfer pump is described in U.S. Published Application 2008/0314548. The system comprises at least (1) a vessel for retaining molten metal, (2) a dividing wall (or overflow wall) within the vessel, the dividing wall having a height H1 and dividing the vessel into a least a first chamber and a second chamber, and (3) a molten metal pump in the vessel, preferably in the first chamber. The second chamber has a wall or opening with a height H2 that is lower than height H1 and the second chamber is juxtaposed another structure, such as a ladle or lauder, into which it is desired to transfer molten metal from the vessel. The pump (either a transfer, circulation or gas-release pump) is submerged in the first chamber (preferably) and pumps molten metal from the first chamber past the dividing wall and into the second chamber causing the level of molten metal in the second chamber to rise. When the level of molten metal in the second chamber exceeds height H2, molten metal flows out of the second chamber and into another structure. If a circulation pump, which is most preferred, or a gas-release pump were utilized, the molten metal would be pumped through the pump discharge and through an opening in the dividing wall wherein the opening is preferably completely below the surface of the molten metal in the first chamber.